How to tune a Stihl 039 carb? (My saw is alive!)

Discussion in 'Chainsaws and Power Equipment' started by Allen Lee, Dec 22, 2015.

  1. Allen Lee

    Allen Lee

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    Hey everybody! As I posted in another topic, I recently bought a saw (Stihl 029 super), the saw blew up, after about 6 hours of operation, due to aftermarket wristpin circlips coming out and now I just put a new bigger Farmertec motor assembly in with new Caber piston rings and OEM wristpin circlips. Well the new motor is a 49mm as opposed to the 47mm that came in the saw. 49mm motor is the same motor that comes in an 039, or at least I am told.
    Long story short, I got the motor running now just need to adjust the carb and was wondering if you guys would share your knowledge with me, I tried the standard adjustment of seating (very softly) the high and low screws and then backing off one turn but I don't really know what to do afterwards, the motor will only idle for a few seconds before it dies, I can keep it running by giving it gas but don't really know where to go for the proper idle (which way to turn the screw and what not).
    Here's some pics of the rebuild.
    [​IMG][​IMG][​IMG][​IMG][​IMG][​IMG]
    Your input is greatly appreciated!
    Thanks all!

    Allen lee
     
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  2. MasterMech

    MasterMech The Mechanical Moderator

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    More or less the same procedure. If the muffler is stock on that 039, it will be harder to hear what's going on.

     
    Last edited: Dec 22, 2015
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  3. MasterMech

    MasterMech The Mechanical Moderator

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    You don't have to shoot for specific numbers with a tach like I did in that vid either. Just listen to what's going on. When setting the low idle speed, the clutch should engage at roughly 3700 rpm. So to get in the ballpark, turn the LA screw in until the chain begins to spin, back off until it stops, crank it back out another 1/4 turn or so (rpms should audibly drop) and you should be close enough to set your L (low mixture) screw appropriately. Turn the L in until the saw begins to stumble, then back it out a 1/4 turn or so. Check your throttle response. If it revs instantly with no hesitation, your good on the L. If it hesitates and then revs, turn it out in 1/8 turn increments until throttle response is crisp. If it dies when you hit the trigger to WOT, then turn the H out a half turn from your 1 turn out initial setting and check again. Still dies? Something is wrong and you need to check the carb and for air leaks.

    Set the H like I did in the vid, listen close for the exhaust note to change from a real clear, clean "scream" to a slightly "buzzy" sound. That buzz is the saw 4-stroking. Once your have it set, you are ready to start cutting wood! Just double check your tune in the wood, the exhaust note should instantly clean up as soon as the engine sees a moderate load and revert back to 4 stroking when the load is removed with the trigger at full throttle.
     
    Last edited: Dec 22, 2015
  4. pantelis

    pantelis

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    No need to tune it , leave it as it is , no matter if die you pull again the rope and it start :D
    ok ok i will stop joking. The video and the explaination that the mastermech post is one and maybe the best of all that i have see-listen and read until now. :yes:

    but if you think that you are not ready to do it or if you afraid better go to a chainsaw mechanic or to a dealer and stay with him to explain you at the first hand what he doing. if you are sure do it yourself. but without to want afraid you if you make sh..... with the H screw its very possible tomorow you post a new thread and ask why the saw need a new piston-cylinder
    just my opinion you can fall it to garbage if you want
     
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  5. Allen Lee

    Allen Lee

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    Very good video, where should I set the LA screw for the standard adjustment? The saw will only idle for a few seconds before it dies.
     
  6. MasterMech

    MasterMech The Mechanical Moderator

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    You can try turning it in, there is no std adjustment. If you can see it contact the throttle lever plate, turn it in until it opens the throttle plate a good amount. If it starts like that, it will probably idle high and start the chain spinning so be careful! Then just back it off until the chain stops and proceed from there. If it refuses to idle after playing with the LA, back the L screw out a half turn and try again.
     
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  7. Allen Lee

    Allen Lee

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    Thanks will try!
     
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  8. Allen Lee

    Allen Lee

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    Tuning worked well! Thanks! I am still working on the high carb set screw, trying to get it just right. Took the saw cutting a little today! Ran good!
     
  9. Kevin in Ohio

    Kevin in Ohio

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    That's a great post and should be made a sticky!
     
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